In the extraction of mineral oil deposits, it is general to differentiate between three recovery phases.
In phase I, the naturally occurring propelling forces are used for transport. The main force used is water pressure which is caused by the pressure of the edge water and/or the expansion of the edge water. The gas pressure of the expanding gas gap and/or the expanding gases dissolved in the oil are also used. In addition, the oil expansion pressure and gravity must be included with the naturally propelling forces.
If the above-mentioned forces are insufficient for the economic transport of the oil and especially, if the edge water is no longer capable of equalizing the pressure drop caused by the transport of oil, then phase II secondary measures are employed. Such secondary measures are, for example, the mechanical control of the pore content by forcing in gas or air or rather gas or water and/or exhausting gas.
A further possibility resides in increasing the surface area of the pore system, e.g., mechanically, by torpedoing, or chemically through the use of acids. A further measure consists of altering the physical forces of the contents and walls of the pores by bacterial activity, heat and especially, by the addition of surface active materials. In the secondary recovery step, these surface active materials are added to the flood water.
The phase II processes are no longer used when the costs of the measures used in this phase equal or exceed the value of the transported oil or products derived therefrom.
Most recently, tertiary transport measures, the so-called phase III methods, have attained particular importance since the extent of the oil recovery from the deposits at the conclusion of phase II is generally only about 33%.
The measures of phase III can be divided into various processes of which the technique of chemical water flooding is of particular importance. The term, chemical water flooding, is understood to mean
(a) polymer flooding, in which particularly polyelectrolytes, such as, partially hydrolyzed polyacrylamides or ionic polysaccharides, are added to the flood water; PA1 (b) surfactant flooding, whereby substances that lower surface tension, especially petroleum sulfonates, are added to the flood water; PA1 (c) alkali flooding, whereby the acidic substances, present in the mineral oil are neutralized by the addition of alkali solutions to the flood water and the surface tension is thereby affected; PA1 (d) micellar flooding, in which high concentrations of surface active materials, especially of petroleum sulfonates, are used in order to incorporate the mineral oil in micelles and to transport it in the form of finely divided emulsions; PA1 (e) emulsion flooding, whereby emulsions are pumped into the deposits and PA1 (f) foam flooding, in which initially a surfactant is forced into the deposits and foam is then formed by the subsequent injection of gas into the deposits.
Detailed literature, dealing with the problems, especially with secondary and tertiary mineral oil transport, can be found in the Kompendium 74/75 des Industrieverlages von Hernhaussen KG, 1975, in which the papers presented at the 24th Meeting of the Deutschen Gesellschaft fur Mineralolwissenschaft und Kohlechemie e.V. (German Association for Mineral Oil Science and Coal Chemistry) are reproduced (especially Page 156 ff.).
It can be seen from the preceding that surface active substances play an important role in the transport of mineral oil, especially in phases II and III. The petroleum sulfonates, which are the surfactants that are primarily used for this purpose, have the advantage of low price but the disadvantage of sensitivity especially towards multivalent cations. Calcium and magnesium salts of these compounds are not water soluble and dissolve preferentially in the oil phase. However, sinc mineral oil and salt deposits are frequently encountered together and the water, found in the deposits, has a high electrolyte content, the abovementioned, cheaper sulfonates can only be used within the limits set by their solubility.
Cationic, surface active materials, such as, for example, quaternary ammonium salts, derivatives of fatty amines and polyamines, have also already been used. However, these compounds have the disadvantage of substantivity or attraction especially towards silicate rock and they lose their activity by adsorption.
The well known non-ionic surface active materials do have the advantage of relative insensitivity towards electrolytes, even if their solubility in water is also reduced by electrolytes, and they do not show the marked substantivity of cationic compounds. This class of compounds, especially the addition products of ethylene oxide with compounds containing active hydrogen, is however, relatively expensive and has limited activity. In addition, the compounds hinder the de-emulsification of the transported oil/water emulsion. Detailed literature concerning the most important surface active substances that have been used up to the present, can be found in the Enzyklopadie der technischen Chemie of Ullman (Ullman's Encyclopedia of Chemical Technology), Vol. 6, Page 568 ff.